If you're like most computer users, your PC or Mac is loaded with a gazillion family photos and other prized documents. Some of you may be sleeping peacefully believing that the external hard drive you picked up at Costco is backing up your data every night, but have you ever checked to see if it's configured correctly? What's really going on inside that black box? And what would happen if your house caught fire? (See the 50 best websites of 2009)

One high-tech  and essentially idiot-proof  alternative is to back up your stuff online. A growing number of companies will automatically sweep your hard drive and keep a copy of the information that is there in the internet "cloud." Many early adopters use Mozy or Carbonite, which allow users unlimited backup space for the cost of a latte each month. For the cost of a lobster, rival sites such as SugarSync offer additional features like non-emergency access to backed-up files  e.g., the ability to update something in your office that you were working on at home. (See five websites you may not know about.)

Once available only to big corporations, off-site automatic backup is starting to catch on with consumers. According to the market-research firm Mintel, 36% of North American computer users surveyed expressed interest in online backup, which, by the way, can only be used by people with high-speed connections.

Thomas Vitale, a Syfy Channel executive, signed up for Mozy in early October, largely to safeguard his trove of family pictures. He and his wife have taken photos of each of their three daughters every day since they were born. Every month or so, he backs up the 25,000 photos, 1,000 videos and other files from nearly 25 years of PC use  which take up about 125 gb on his home computer in Manhattan  on an external hard drive that is not connected to his computer in order to keep it safe from viruses. In between these external-drive sessions, he relies on Mozy, which for $5 a month moseys along at a pace that will probably require two or three months to back up his entire hard drive. Vitale says the long upload time isn't problematic since Mozy works in the background and does not noticeably slow down his computer. Mozy's low price also helps make up for its lack of speed. (The same amount of data space on SugarSync, for example, would cost Vitale $25 a month.)

OnlineBackupsReview.com and backupreview.info are good places to begin comparison shopping. Depending on the provider, data recovery might not be immediate, and customer service can be maddening. Some companies have quit the space. Earlier this year, for example, Hewlett-Packard said it would discontinue Upline; Yahoo did the same with Briefcase. Eric Nagel, who runs onlinebackupsreview.com, said that while companies gave subscribers at least a month's notice, a complete transition may take several weeks.

"Despite cons such as poor customer service and slow initial upload, online backup still protects your data better than something in your home because it's in a secure, off-site environment, safe from theft, fire, flood and other mishaps," Nagel said.

Even so, apprehension about backing up files online has led many customers like Vitale to take a belt-and-suspenders approach, using the cloud as a smart way to add an extra layer of security while still relying on traditional backups like external hard drives, thumb drives and archival DVDs.

Experts note that no single solution is perfect, but that doesn't mean computer users should give up and do nothing. "How you select to do backup isn't nearly as important as doing it," says Mintel senior analyst Bill Hulkower. "If I'm a dentist, the first step is to get you to floss. Once you start, then you can decide the best product."